The field of the invention is exhaust fans, and more particularly, exhaust fans for commercial kitchens.
Exhaust fans for kitchen ventilation applications must be capable of handling hot, grease-laden air The fan motor must be kept out of the air stream, which can reach temperatures of up to 300.degree. F., and effectively cooled to prevent premature failure. In addition, the motor must be enclosed to prevent grease build-up on the motor which acts as a thermal insulator and prevents it from being properly cooled. To prevent damage to the roof which supports the exhaust fan, it should contain and properly drain all grease removed from the airstream. This requires that the fan components be sealed such that any grease which collects inside the fan will drain only through a drain trough into a grease collection and removal system.
There are many types of exhaust fans in common use in restaurants. An "upblast" exhaust fan is designed for roof mounting directly on top of the exhaust stack which extends upward from the interior of the building, and it directs the grease-laden air upward, away from the roof. Upblast exhaust fans typically have an integral grease drainage system and grease trap or removal system, and they are usually cleaned by hinging them back from the exhaust stack. A "utility set" exhaust fan is also usually mounted on the roof of the restaurant and its discharge is orientated to direct exhausted air away from the roof. The housing of the fan is generally sealed and has a drain at the bottom to remove grease and moisture. These fans are usually cleaned by removing access panels or duct extensions. Access to the fan and associated duct system is very limited and quite difficult at best. An "inline" exhaust fan is typically mounted in the exhaust duct which is located inside the building. It is used when the fan cannot be mounted outside, either on the roof or on an outside wall. Inline exhaust fans are typically cleaned by removing them from the duct system or through access openings in the fan or duct system. Grease and moisture are removed from the fan by a drain located at the bottom of the fan's housing. In all applications of these various styles of exhaust fans, the build-up of grease on the fan components exposed to the cooking gases is relentless and is a significant maintenance problem.
All components of a ventilation system are designed to operate in balance with each other to properly capture, contain, and remove the cooking gases and heat. Grease build-up on the fan will reduce its aerodynamic performance which unbalances the system, affecting its operation, or efficiency. Additionally, the build-up of grease on exhaust fan components can create health and fire hazards if not routinely removed. Grease build-up, if not removed will also create mechanical unbalance and excessive vibration. This excessive vibration will create noise in the system and reduce the life of the fan. Accordingly, the removal of grease build-up on exhaust fan components is a scheduled procedure that is performed regularly as part of a maintenance program.
For an exhaust fan on a typical restaurant, cleaning may be required every three to six months depending on the application. Removing the grease build-up on prior designs typically requires a pre-soak with strong cleaning solutions, high pressure hot water rinse and scraping. Typically, this cleaning process needs to be repeated several times to remove the grease and baked on deposits. The harsh cleaning solutions cause damage to the system's components and the roofing, and may be hazardous for cleaning personnel. The large quantity of hot water required for cleaning must be contained and removed from the roof of the restaurant. Scraping the unit to remove baked on deposits can cause damage to the fan by removing balance weights or bending the wheel or shaft. Removing these weights will cause excessive vibration. Excessive vibration will cause noise in the structure below and lead to premature fan failure. A typical cleaning of an upblast exhaust fan may take 2 to 3 hours to perform and become very costly due to the time, chemicals and hot water used and the potential for damage to the roof.